[3] Eilish performed a concert at the Sant Jordi Club in Barcelona on March 9, and the following day Rosalía posted a picture of both on social media and stated "can't wait to finish our song.

[citation needed] In April 2020 Rosalía told Zane Lowe that while in lockdown due to the COVID-19 pandemic she had been working on the track for over two consecutive weeks.

[citation needed] In January 2021 Finneas expressed admiration for a Billboard article about the bilingual collaborations the magazine anticipated in 2021.

[13] Producer Finneas O'Connell told the press that the song went through a lot of stages, something quite rare since he and his sister usually keep the first impression as the final sound.

Although the track was scheduled to be released during summertime in 2020, the production was revamped during that time and the final verses were added by Eilish with a little help from other O'Connell family members.

[17] Steffanee Wong of Nylon stated that the song is sung entirely a capella, and mentioned it had "sparse nature sounds and atmospheric synths forming a misty backdrop, as Eilish and Rosalía do vocal gymnastics around each other, sometimes in English but mostly in Spanish.

"[16] Patrick Hosken of MTV said it features a "dreamlike plane where slight shifts in mood and atmosphere are guided by powerful vocal moments from each.

[21] Writing for Pitchfork, Eric Torres commented that "Eilish and Rosalía's rich harmonies create a supernal vibe entirely their own, amounting to a decent if inessential addition to their catalogs".

[26][27][28] The music features Eilish and Rosalía alone in a dark room, lit only by a moving spotlight, singing into a shadowy and stormy void.